In electronic control devices such as an inverter or a servo, the electronic control function is realized by integrating various types of active components and passive components on a circuit board. Especially in such electronic control devices such as an inverter or a servo, power control is executed by using a large capacity diode, a transistor, or the like.
The conventionally, so-called DBC substrate or metal substrate, has been used as a substrate for a circuit using semiconductor elements emitting a large quantity of heat such as those for power. The DBC substrate comprises ceramics and a conductive material, with such materials as alumina ceramics and aluminum nitride ceramics used for the ceramic insulating material. Also copper is often used as a conductor in the DBC substrate, and the thickness is 0.3 mm in the typical specification.
On the other hand, as a metal base substrate, a circuit conductor is formed via an insulating layer made of an organic insulating material on a top surface of a base metal plate, and generally such metals as aluminum, copper, or iron are used as the material. In the conductor formed on a metal base substrate, generally a thickness of copper foil is around 0.1 mm, and a circuit on the substrate is generally formed by means of etching.
However, the etching system described above is suited to mass production because, for instance, a mask is manufactured, but it causes increase of cost when producing many types of product in a small lot respectively. In addition, when a conductor pattern is formed by etching, the thickness of the conductor becomes larger because of effects by side etching with the pattern precision lowered, and furthermore when mounting a bare chip on a substrate, a heat spreader is often used, which in turn results in increase of required parts.
Also when a thickness of a conductor becomes larger, it becomes difficult to form a fine pattern such as a control circuit due to side etching. Furthermore as a conductor's thickness is at most around 0.3 mm, there is a limit in amplitude of a current applied to the circuit, which makes it impossible to apply a large current, and even if a thickness of a conductor is made larger, sometimes such defects as warping occur in the substrate.